Mechanism of action of spironolactone on cortisol production by guinea pig adrenocortical cells.

Studies were done to determine the mechanism(s) of action of spironolactone (SL) and of its deacetylated metabolite, 7 alpha-thio-SL, to inhibit cortisol secretion by guinea pig adrenocortical cells in vitro. Preincubation of cells at 37 degrees C with SL or with 7 alpha-thio-SL caused a time-dependent decline in subsequent ACTH-stimulated cortisol secretion. In the absence of a preincubation, neither compound affected cortisol production, indicating the need for production of an active metabolite. When the 17 alpha-hydroxylase inhibitor, SU-10'603, was included during the preincubation period, neither SL nor 7 alpha-thio-SL decreased cortisol secretion, indicating the involvement of the 17 alpha-hydroxylase in the activation of both compounds. By contrast, neither the 11 beta-hydroxylase inhibitor, metyrapone, nor the cholesterol sidechain cleavage inhibitor, aminoglutethimide, diminished the effects of SL or of 7 alpha-thio-SL on cortisol secretion. Preincubation of cells with SL or 7 alpha-thio-SL also decreased the conversion of exogenous progesterone to cortisol, but did not affect cortisol production from the 17 alpha-hydroxylated substrates, 17 alpha-hydroxyprogesterone and 11-deoxycortisol, suggesting that only 17 alpha-hydroxylation was impaired. In addition, there was a decline in 17 alpha-hydroxylase activity in microsomes isolated from cells preincubated with SL or with 7 alpha-thio-SL, but no change in microsomal 21-hydroxylase or in mitochondrial 11 beta-hydroxylase and cholesterol sidechain cleavage activities. The results indicate that the direct effects of SL and of 7 alpha-thio-SL on the adrenal cortex to decrease cortisol production result from the selective inhibition of 17 alpha-hydroxylation. Since 17 alpha-hydroxylase activity is apparently required for the activation of both compounds, suicide inhibition of the enzyme may be the mechanism of action.